Through the use of image processing techniques, it can be possible to generate a high resolution image from a plurality of lower resolution images. Optical dithering allows the formation of a high-resolution image for display on a display device from two or more lower resolution images. For example, it is possible to create a high resolution image with a resolution of 1024×768 pixels from a 512×384 pixel rectilinear display device by optically moving the lower resolution display device in four half-pixel steps. The same high-resolution image can be created by moving a 1024×384 diamond display device in two half-pixel steps. The high-resolution image can therefore be formed from four quarter-resolution images or two half-resolution images.
Using optical dithering, it is possible to take a sequence of high-resolution images, such as from a high definition television feed, decompose each of the high-resolution images into multiple lower resolution images, and display the lower resolution images on the display device, simulating the high-resolution images of the high definition television feed. However, rather than using a display device that is capable of displaying the high resolution images at full resolution, the display device is only capable of display images at a half or quarter (or lower) resolution of the high resolution image.
The use of lower resolution display devices in place of a high-resolution display device can be advantageous since display devices with large pixel counts tend to be more expensive than smaller pixel count display devices. a large pixel count display device can be more expensive since they often require the use of more advanced manufacturing processes as well as having a typically lower yield rate. Additionally, adjunct circuitry needed to support the large pixel count display device is often correspondingly more expensive since they may have stricter tolerance requirements, greater data rate requirements, faster memories, and so forth. The use of optical dithering can permit the use of a lower resolution display device, while providing comparable image quality.
However, image quality can be a problem if there is motion present in an image being displayed with a display device using optical dithering techniques. The presence of motion in the image being displayed can lead to undesired artifacts when the high resolution image is being decomposed into the plurality of lower resolution images. The decomposition of the high resolution image into the plurality of lower resolution images is known as down-sampling. Down-sampling an image containing motion can lead to aliasing, which is a distortion caused by an interaction between signal frequency and sampling frequency. Too much aliasing can lead to an unacceptable image.
One technique that can be used to help remove the decomposition artifacts is to filter the high resolution image prior to the down-sampling operation. a low-pass filter, also known as an anti-aliasing filter, with appropriately selected frequency characteristics, can be used to filter the high resolution image prior to down-sampling and prevent (or reduce) the occurrence of aliasing.
One disadvantage of the prior art is that the use of the low-pass filter can result in a softening of the image in portions of the image without motion. Image softening can negate the performance gained by using high resolution images. For example, an over aggressive low-pass filter may result in an image that is not significantly better than standard definition television, even if the television is capable of displaying high definition images.